JP3251825B2 - Noise canceller circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television video signal processing circuit, and more particularly to a noise canceller circuit for removing an edge noise component of a luminance signal, such as a home video tape recorder (VTR). Used for video signal recording and playback devices.

[0002]

2. Description of the Related Art For example, in a home VTR for recording / reproducing a television video signal of the NTSC system, a recording signal processing system converts a luminance signal component of the video signal into a low carrier FM signal and converts the color of the video signal into a color signal. The signal component is
The signal is converted into a signal having a frequency lower than that of the M signal (a low-frequency converted chrominance signal, a carrier is, for example, 629 KHz), and the low-frequency converted chrominance signal is superimposed on the low carrier FM signal and recorded on a video tape. The reproduction signal processing system separates the low carrier FM signal and the low-frequency conversion chrominance signal from the reproduction signal, FM-demodulates the luminance signal component from the low carrier FM signal, and converts the low-frequency conversion chrominance signal to 3.5.
It is converted to a carrier color signal of 8 MHz. An edge noise countermeasure circuit for removing an edge noise component of the luminance signal is inserted in the luminance signal reproducing system.

FIG. 5 shows an example of a conventional edge noise countermeasure circuit, and FIG. 6 shows an example of an operation waveform thereof. In the first noise canceller circuit 61 at the preceding stage, the input signal (reproduced luminance signal) is branched into two, and one of the branched signals (main signal) is added to the adder (superimposed circuit).
611, and the other branch signal is input to an HPF (high-pass reactor) 612 to extract a high-frequency signal.

[0004] The high-frequency signal extracted in this way is limited in amplitude by a limiter circuit 613 to extract a noise component. This noise component is converted to an LPF (low-pass reactor) 614.
After the high-frequency component is removed and the phase of the main signal is adjusted, the signal becomes the subtraction input of the addition circuit 611. Accordingly, the addition circuit 611 adds the main signal and the LPF output signal, and outputs a main signal (luminance signal) from which the noise component has been canceled.

On the other hand, in the second noise canceller circuit 62 at the subsequent stage, the input signal (luminance signal) from the first noise canceller circuit 61 at the previous stage is branched into two, and one branch signal (main signal) is added to the adder circuit. (Superposition circuit) 6
21 and the other branch signal is HPF 622
And a high-frequency signal is extracted.

The high-frequency signal extracted in this manner is subjected to amplitude limitation by a limiter circuit 623 to extract a noise component. The noise component is input to an LPF 624, where the high-frequency component is removed, and the noise component is phase-shifted with the main signal. After the matching is performed, it becomes a subtraction input of the adding circuit 621. Accordingly, the addition circuit 621 adds the main signal and the LPF output signal, and outputs a main signal (luminance signal) from which noise components have been canceled.

[0007] In a display image of a video signal, noise of a flat portion (a large-area image portion corresponding to a display portion such as a sky or a wall) which is visually noticeable is low in a low-frequency signal near 1 MHz. It is known to concentrate on levels.

Therefore, of the two noise canceller circuits 61 and 62, the first noise canceller circuit 6
The circuit characteristic of No. 1 is included in the rising edge and the falling edge of a large-amplitude rectangular wave luminance signal as shown in FIG.
The setting is made so as to cancel a noise component having a minute amplitude near MHz.

On the other hand, the circuit characteristics of the second noise canceller circuit 62 are the same as those of the first noise canceller circuit 6.
The setting is made so as to cancel a noise component having a very small amplitude higher than one.

Here, the two limiter circuits 613,
If the limiter level of the limiter circuit 623 is set to L1, the time width of the region where the limiter circuit 613 is saturated (the portion where the edge noise remains) is t1, and the time width of the region where the limiter circuit 623 is saturated (the portion where the edge noise remains) is t1. t2.

In this case, t1 >> t2, and (t
Since the second noise canceller circuit 62 at the subsequent stage operates during the period of 2-t1), apparently the time during which edge noise remains is reduced to t2.

However, as described above, the circuit characteristics of the second noise canceller circuit 62 are set so as to cancel out noise components having a higher frequency than the first noise canceller circuit 61 and have small amplitudes. The noise component near 1 MHz, which is most sensitive to the noise, cannot be canceled sufficiently, and the effect of improving the residual edge noise is small.

[0013]

As described above, in the conventional noise canceller circuit, the time during which the edge noise remains is apparently shortened, but the most sensitive is the human eye.
There has been a problem that noise components in the vicinity of MHz cannot be sufficiently canceled.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a noise canceller circuit which can enhance the effect of improving the residual edge noise and can sufficiently cancel a noise component near 1 MHz. And

[0015]

A noise canceller circuit according to the present invention comprises: an addition circuit for inputting a luminance signal of a television video signal as an addition input; a signal into which the luminance signal is branched; A high-pass reactor for extracting a signal; an edge detection circuit for receiving a signal obtained by branching the luminance signal, detecting an edge thereof and outputting an edge detection pulse signal having a predetermined width; A variable limiter circuit provided to extract a noise component by limiting the amplitude of a high-frequency signal input from a device, wherein the limiter level is temporarily increased by an edge detection pulse signal input from the edge detection circuit; A low-pass reactor that receives an output signal of the limiter circuit and supplies the output signal as a subtraction input of the adding circuit.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a noise canceller circuit used in a luminance signal reproducing system in an NTSC home VTR according to an embodiment of the present invention.

The reproduction signals correspondingly reproduced by the two video heads 10a and 10b are amplified by the pre-reproduction amplifier circuits 11a and 11b, respectively, and then alternately selected by the switcher circuit 12 to become continuous signals. .

The output signal of the switcher circuit 12 is H
The signal is input to the PF 13, where the color signal component (low-frequency conversion color signal) is removed, and the luminance signal component (low carrier FM signal) is extracted. The low carrier FM signal is subjected to drop-out compensation by a drop-out compensator (DOC) 14.

The output signal of the DOC 14 is subjected to FM demodulation by an FM demodulation circuit 16 after the level fluctuation is suppressed by a limiter circuit 15, and a luminance signal component is extracted. After the characteristics of the luminance signal component are corrected by the de-emphasis circuit 17, the carrier component of the FM signal is removed by the LPF 18 and time adjustment (transmission time adjustment with the color signal reproduction system) is performed. After passing through one noise canceller circuit 20 which is an edge noise countermeasure circuit, it is input to an output amplifier circuit 19.

FIG. 2 shows an example of the noise canceller circuit 20 in FIG. The noise canceller circuit 20 shown in FIG. 2 includes an addition circuit 21 to which a luminance signal output from the LPF 18 is input as an addition input, and an H for receiving a signal obtained by splitting the luminance signal and extracting a high-frequency signal thereof.
PF22 and a signal obtained by splitting the luminance signal are input,
An edge detection circuit 23 that detects the edge and outputs an edge detection pulse signal of a predetermined width, and an edge detection circuit that is provided to extract the noise component by limiting the amplitude of the high-frequency signal input from the HPF 22 and input from the edge detection circuit 23 A variable limiter circuit 24 in which the limiter level is temporarily increased by the edge detection pulse signal, and a variable limiter circuit 24
And an LPF 25 to which the output signal is inputted and which supplies the output signal as a subtraction input of the addition circuit 21.

An example of the variable limiter circuit 24 is provided to amplify a high-frequency signal input from the HPF 22, and the gain is temporarily controlled to be small by an edge detection pulse signal input from the edge detection circuit 23. It comprises a variable gain amplifier 241 and a limiter circuit 242 for limiting the amplitude of a high-frequency signal input from the variable gain amplifier 241 and extracting a noise component.

FIG. 3 shows an example of the edge detection circuit 23 in FIG. An edge detection circuit 23 shown in FIG. 3 is provided with an HPF 231 to which a luminance-branched signal output from the LPF 18 is input and to extract a high-frequency signal thereof,
The output signal of F231 is input as a comparison voltage and is compared with each of the reference voltages Vref and -Vref.
2, 233.

FIG. 4 shows the noise canceller circuit 2 of FIG.
5 shows an example of an operation waveform of the edge detection circuit 23 of FIG. Here, the noise canceller circuit 2 shown in FIG.
0 and the operation of the edge detection circuit 23 of FIG.
This will be described with reference to the waveforms shown in FIG.

The input signal (reproduced luminance signal) of the noise canceller circuit 20 is branched into three, the first branch signal (main signal) becomes the addition input of the addition circuit (superposition circuit) 21, and the second branch signal Is input to the HPF 22, and the third
Is input to the edge detection circuit 23.

The HPF 22 extracts the high-frequency signal of the input signal, the amplitude of the high-frequency signal is limited by a variable limiter circuit 24, and a noise component is extracted. After being removed and phase-matched with the main signal, it becomes a subtraction input of the addition circuit 21.

On the other hand, the edge detection circuit 23 detects an edge of the input signal and outputs an edge detection pulse signal having a predetermined width. Then, according to the edge detection pulse signal,
Since the gain of the variable gain amplifier 241 is temporarily controlled to be small, even if the limiter level of the limiter circuit 242 is constant, the limiter level of the variable limiter circuit 24 is equivalently controlled to be temporarily large. As a result, the limiter level of the limiter circuit 242 temporarily increases from L1 in the normal state to L2.

The addition circuit 21 adds the main signal and the signal that has passed through the variable limiter circuit 24 and the LPF 25, and outputs a main signal (luminance signal) from which noise components have been canceled.

The noise canceller circuit 2 as described above
Since the operation of 0 causes the limiter level of the limiter circuit 242 to temporarily increase from L1 in a normal state to L2,
The time width of the region where the limiter circuit 242 is saturated (the portion where the edge noise remains) can be greatly shortened from t2 in the conventional example, and the effect of improving the remaining edge noise is increased.

In this case, the circuit characteristic of the noise canceller circuit 20 is 1 MH included in the rising edge and the falling edge of a large amplitude rectangular wave luminance signal as shown in FIG.
Since the noise component having a small amplitude near z is set to be canceled, the noise component near 1 MHz, which is most sensitive to human eyes, can be sufficiently canceled.

In the above embodiment, the noise canceller circuit is used in the reproduction signal processing system of the VTR. However, the noise canceller circuit may be inserted in the luminance signal processing stage in the recording signal processing system. Is possible,
In this case, even if the S / N ratio of the luminance signal is low, a noise component having a small amplitude near 1 MHz can be canceled. In the above-described embodiment, the V signal for recording and reproducing a video signal is used.
Although the TR is taken as an example, the present invention can be similarly applied to a device exclusively for reproducing video signals.

[0031]

As described above, according to the noise canceller circuit of the present invention, the effect of improving the remaining edge noise can be enhanced, and the noise component around 1 MHz can be sufficiently canceled.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a part of a luminance signal reproducing system in a home VTR according to a first embodiment of a video tape reproducing device of the present invention.

FIG. 2 is a block diagram showing an example of a noise canceller circuit in FIG. 1;

FIG. 3 is a block diagram showing an example of an edge detection circuit in FIG. 2;

FIG. 4 is a waveform chart showing an operation example of the noise canceller circuit of FIG. 2 and the edge detection circuit of FIG. 3;

FIG. 5 is a block diagram showing an example of a noise edge countermeasure circuit inserted into a luminance signal reproduction system in a conventional home VTR.

FIG. 6 is a waveform chart showing an operation example of the noise edge countermeasure circuit of FIG. 5;

[Explanation of symbols]

 10a, 10b: video head, 11a, 11b: reproduction preamplifier circuit, 12: switcher circuit, 13: HPF, 14: DOC (dropout compensation circuit), 15: limiter circuit, 16: FM demodulation circuit, 17: de・ Emphasis circuit, 18 LPF, 19 output amplifier circuit, 20 noise canceller circuit, 21 addition circuit, 22 HPF, 23 edge detection circuit, 231 HPF, 232, 233 voltage comparison circuit, 24 variable Limiter circuit, 241, variable gain amplifier, 242, limiter circuit, 25, LPF.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/21 H04N 5/91-5/956

Claims (2)

(57) [Claims] An adder circuit for inputting a luminance signal of a television video signal as an addition input; a high-pass reactor for receiving a signal obtained by splitting the luminance signal and extracting a high-frequency signal; A signal into which a luminance signal is branched is input, and an edge detection circuit that detects an edge thereof and outputs an edge detection pulse signal having a predetermined width, and amplifies a high-frequency signal input from the high-pass reactor.
And an edge input from the edge detection circuit.
The gain is temporarily controlled to be small by the detection pulse signal.
A variable gain amplifier, and a high-frequency signal input from the variable gain amplifier;
A limiter circuit for taking out the noise components Te, before inputs the output signal of the cut emitter circuit, noise canceller, wherein an output signal that comprises a low-pass furnace filter supplied as a subtraction input of the adder circuit circuit. 2. The noise canceller according to claim 1, wherein :
The circuit is a recording signal processing system of the video signal recording / reproducing device.
Or a noise canceller circuit used in a reproduction signal processing system .